1. Field of the Invention
The present invention relates to a phase shift data transfer system for phased array antenna apparatuses employed in transferring phase shift data to a control circuit for a phase shifter in each of the antenna elements.
2. Description of the Prior Art
FIG. 1 is a schematic representation of the configuration of a plurality of elements of a commonly used phased array antenna apparatus and the direction of a beam formed by this antenna apparatus. A plurality of antenna elements (101), (102), . . . (10i), . . . (10n) are located in the X-Y plane. Each antenna element is provided with a phase shifter having a predetermined phase shift capability so that the phased array antenna apparatus forms a beam in a desired direction. The coordinates of a point on a beam in the desired direction are assumed as (X.sub.B, Y.sub.B, Z.sub.B).
In operation, the phase of a radio wave transmitted or received by each of antenna elements (101) to (10n) is set according to the following equation (1) so that the set of antenna elements (101) to (10n) may transmit or receive a beam of radio waves in a desired direction: EQU .phi..sub.i =k(x.sub.i .multidot.X.sub.B +y.sub.i .multidot.Y.sub.B)(1)
wherein i=1, 2, 3, . . . n (n is the number of antenna elements), k is a constant determined by the radio wave frequency, .phi..sub.i is the phase shift data in the phase shifter in antenna element (10.sub.i), and x.sub.i and y.sub.i are the x coordinate and the y coordinate of antenna element (10.sub.i), respectively. Assuming that R is a constant, the following equation (2) is obtained: EQU X.sub.B.sup.2 +Y.sub.B.sup.2 +Z.sub.B.sup.2 =R.sup.2 ( 2)
In order to allow the phased array antenna apparatus to form a beam of radio waves in a desired direction, the amount of phase shift to be set for antenna elements (101), (102), . . . , (10n) is sequentially computed in accordance with the equation (1). Once the computation of the amount of phase shift to be given to one phase shifter is completed, the result of the computation is transferred as phase shift data to the corresponding phase shifter where such data is held until the next new phase shift data is transferred thereto. The amount of phase shift to be given to another phase shifter is then computed and the result of the computation is also transferred to the corresponding phase shifter in which it is set. Thus, the computation of the amount of phase shift is sequentially conducted for every phase shifter. Once obtained, the result of computation is then transferred to a corresponding phase shifter and set and held there until the next new phase shift data is transferred thereto.
Thus, a predetermined amount of phase shift is set for the phase shifter in every antenna element to allow the phased array antenna apparatus to form a beam of radio waves in a desired direction.
As described above, in the prior art phased array antenna apparatus, phase shift data are sequentially computed in accordance with the equation (1) and transferred to the phase shifters in antenna elements (101) to (10n) to be set therein. Therefore, assuming that the time required to compute each phase shift data is Tc and that the time required to transfer each phase shift data to a corresponding phase shifter is Tt, the time (Tall) given by the equation (3) is required to compute and transfer all such phase shift data to all the phase shifters: EQU Tall=n(Tc+Tt) (3)
Since the time Tc and the time Tt are constant for each one of antenna elements (101) to (10n), the greater the number of antenna elements, the longer the time Tall required to compute the phase shift data and then set a predetermined amount of phase shift in all the phase shifters.